1. Field of the Invention
This invention concerns novel, unique and useful coal ash fertilizer compositions and a method for manufacturing of such compositions. It has been found that by performing certain chemical reactions that particulate coal residue can be converted into valuable fertilizers. Depending on the specific reactions involved, the coal residue can be made into a slow acting fertilizer or a fast acting fertilizer and/or a combination of the two. In addition to having present, after chemical modification, the major elements needed for growth of plants, for example, nitrogen, phosphorous and potassium, coal ash itself has present in it many of the minor and micro nutrients needed for effective plant growth.
Coal is the most widely distributed fuel in the United States and is found in 38 states. The nation's total coal reserves have been estimated at about 4 trillion tons, nearly half of which is thought to be recoverable reserves. The coal from the wide range of locations across the country include fuels varying significantly with respect to heat content, ash content and chemical properties. Coal combustion results in a residue consisting of the inorganic mineral constituents in the coal and some organic matter which is not wholly burned. The inorganic mineral constituents, whose residue is ash, make up from 3 to 30 percent of the coal. During combustion, this ash is distributed into two parts, bottom ash collected from the bottom of the boiler unit, and fly ash, most of which is collected by air pollution control equipment. The distribution of ash between the bottom and fly ash fraction is a function of the boiler type, coal type, and whether or not a wet or dry bottom furnace is utilized. Fly ash makes up from 10% to 85% of the coal ash residue and occurs as spherical particles, usually ranging in diameter from 0.5 to 100 microns. The bottom ash, composed primarily of coarser, heavier particles than the fly ash, ranges from gray to black in color and is generally angular with a porous surface. If it is collected as a slag, these slag particles generally are black, angular and have a glass-like appearance.
Petrographic analysis has shown that glass is the primary component of ash. Other components of the ash include magnetite, hematite, carbon, mullite, and quartz. The major chemical constituents of ash are primarily silica, alumina, iron oxide, and calcium oxide. Minor elements present include magnesium, titanium, sodium, potassium, sulfur and phosphorus. They comprise from 0.5% to 3.5% by weight of the ash. Ash also contains trace concentrations of from 20 to 50 different elements including antimony, arsenic, barium, beryllium, boron, copper, fluorine, lead, manganese, mercury, molybdenum, nickel, selenium, tellurium, thallium, tin, uranium, vanadium, cobalt and zinc.
If you compare this list of elements found in coal ash residues to the list of elements required for plant nutrition, you find considerable overlap. Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur are the elements of which proteins, hence, protoplasm, are composed. In addition to these six, there are fourteen other elements which are essential to the growth of some plant or plants; calcium, magnesium, potassium, iron, manganese, molybdenum, copper, boron, zinc, chlorine, sodium, cobalt, vanadium and silicone. While all are not required for all plants, all have been found to be essential to some. These mineral elements, in addition to phosphorus and sulfur, usually constitute what is known as the plant ash, or the minerals remaining after the burning off of carbon, hydrogen, oxygen and nitrogen. Each of the 20 elements play a role in the growth and development of plants, and when present in insufficient quantities, can reduce growth and yields.
When comparing the elements of coal ash residues and the required elements for plant growth, it is amazing to find that only sufficient quantities of nitrogen, phosphorus and chlorine are not available in fly ash residues and perhaps sufficient potassium depending on the origin of the coal ash. Considering the great diversity of elements found in nature, overlap between coal ash residues and what is required for effective growth of plants is remarkable. By suitable chemical modifications to introduce larger quantities of nitrogen and phosphorus and small amounts of chlorine, if required, these chemically modified coal ash residues will make excellent fertilizers at very low cost because unlike commerical fertilizers, they contain all the necessary elements for plant growth.
Tables I and II show the variation in coal ash composition with coal rank and the chemical characteristics of fly ash and bottom ash from the particular coal region in the United States.
TABLE I ______________________________________ VARIATION IN COAL ASH COMPOSITION WITH COAL RANK Chemical Coal Rank, Percent Constituent Anthracite Bituminous Subbituminous Lignite ______________________________________ SiO.sub.2 48-68 7-68 17-58 6-40 Al.sub.2 O.sub.3 25-44 4-39 4-35 4-26 Fe.sub.2 O.sub.3 2-10 2-44 3-19 1-34 TiO.sub.2 1.0-2.0 0.5-4 0.6-2 0.0-0.8 CaO 0.2-4 0.7-36 2.2-52 12.4-52 MgO 0.2-1 0.1-4 0.5-8 2.8-4 Na.sub.2 O -- 0.2-4 -- 0.2-28 K.sub.2 O -- 0.2-4 -- 0.1-1.3 SO.sub.3 0.1-1 0.1-32 3.0-16 8.3-32 ______________________________________
TABLE II ______________________________________ TRACE ELEMENTS IN COAL AND COAL ASH FROM DEPOSITS AROUND THE WORLD Coal Ash Element (ppm) (ppm) ______________________________________ Antimony 10-30 100-3,000 Arsenic 0.8-500 280-10,000 Barium 2-257 18-2,200 Beryllium &lt;0.1-40 1-4,000 Bismuth 0-100 0-2,000 Boron 15-356 52-10,000 Chlorine 30-560 Chromium &lt;0.1-50 &lt;0.1-7,400 Cobalt &lt;0.4-34 &lt;5-2,000 Copper 2.6-185 10-1,200 Fluorine 40-480 Gallium &lt;1.4-100 10-3,200 Germanium &lt;0.4-50 9-47,000 Iodine 1.11 Lanthanum &lt;1.5-40 &lt;30-700 Lead 25-3,000 200-31,000 Manganese 9-&gt;5,000 100-22,000 Mercury 0.001-300 Molybdenum &lt;0.7-200 &lt;5-6,000 Nickel 0.42-&gt;60 &lt;5-16,000 Palladium 0.2 Platinum 0.7 Rhodium 0.02 Silver 0-3 0-60 Strontium 0-100 0-&gt;1,000 Scandium 60-400 Tin &lt;0.1-300 0.4-6,000 Titanium 95-2.320 100-35,000 Uranium 0-24,000 6-1,650 Vanadium &lt;1.4-&gt;100 &lt;10-25,000 Yitrium &lt;0.1-49 &lt;10-2,000 Zinc 7.6-2,000 115-21,000 Zirconium 0-140 0-7,000 ______________________________________
It should be recognized that the diversity of the chemical composition of coal ash varies from region to region, therefore, depending on the origin of the coal, different chemical reactions should be carried out to obtain an efficient fertilizer.
To achieve an effective fertilizer, it is necessary to transform some of the elements found in coal ash residues into a desirable chemical moieties. The major elements of a fertilizer are nitrogen, phosphorus and potassium. The known types of nitrogen containing fertilizers are the following: ammonium sulfate, anhydrous ammonia, ammonium chloride, ammonium nitrate, ammonium nitrate with lime, ammoniated superphosphate, monoammonium phosphate, diammonium phosphate, ammonium phosphate-sulfate, calcium nitrate, calcium cyanamide, potassium nitrate, sodium nitrate, urea, urea-sulfur, urea-phosphate, sulfur coated urea, urea-formaldehyde, metal ammonium phosphates, for example, magnesium ammonium phosphate, oxamide, crotonylidene diurea, isobutylidene diurea, dicyanadiamide and thiourea. The second major element is phosphorus. There are two types of phosphorus, an organic type and an inorganic type. The organic types are: phospholipids, nucleic acids, and inositol phosphates; inorganic types are collectively called orthophosphates; these are phosphoric acid, superphosphoric acid, calcium orthophosphates, ammonium phosphates, nitric phosphates, potassium phosphates, dicalcium phosphates and calcium metaphosphates and the so called polyphosphates.
With respect to the third major elements, potassium, you can have potassium, which is slowly available, and these include potassium tied up with various clay soils, or you can have water soluble potassium compounds present as potassium halides, nitrates, sulfates or double salts containing potassium compounds. These and other type fertilizers containing the major elements required for plant growth are detailed in a textbook entitled "Soil, Fertility and Fertilizers", Third edition, by Samual L. Tisdale and Werner L. Nelson, published by MacMillen Publishing Co., Inc., New York 1975. This reference is hereby incorporated into the body of this invention.
In order to have a better understanding of this invention, it is important to understand how each of the major nutrient elements for plants functions. Nitrogen is absorbed by plants primarily in the form of nitrates, although smaller amounts of the ammonium ion and urea can also be absorbed. An adequate supply of nitrogen is associated with vigorous vegetable growth and a deep green color. When plants are deficient in nitrogen, they become stunted and yellow in appearance. Phosphorus is generally absorbed as the primary orthophosphate (H.sub.2 PO.sub.4.sup.-1) and smaller amounts of the secondary orthophosphate (HPO.sub.4.sup.-2). Other forms of phosphorus can be assimilated into a plant, among which are pyrophosphates and metaphosphates. They are absorbed by plant roots. These latter materials are polyphosphates hydrolyzed slowly. Phosphorus is associated with increased root growth and hastens plant maturity. Potassium is generally absorbed as the potassium ion. The requirement for potassium in plants is quite high. Potassium deficiencies greatly reduce crop yields and decrease the resistance to certain plant diseases. Photosynthesis is decreased, thus carbohydrates are less available. Calcium is also required by high plants and it is absorbed principally as the calcium ion. Deficiency results in failure of the terminal buds of the plants to develop. Magnesium is responsible for the production of chlorophyll. The chlorophyll molecule contains a coordinated magnesium ion needed for photosynthesis. Sulfur is absorbed by plant roots as the sulfate ion, it is almost exclusively reduced to disulfide and the mercapto group. The deficiency of sulfur has a pronounced retarding effect on plant growth. Boron is generally absorbed in the ionic oxygenated form, while iron is utilized from complex organic materials. The other micro-nutrients requirements are not well studied and consequently will not be discussed.